In this respect I doubt not that the Fabrician genus _Hexapus_, adopted and figured by De Haan, will be found to agree with it, although it is very remarkable that the anomalous condition of this part never excited any particular attention on the part of either of these distinguished naturalists; and De Haan describes Fabricius's species, _Hexapus sexpes_, as if there were nothing especial or abnormal in a Decapod having only six pairs of legs besides the claws.

To this we may answer that the occurrence of the Zoea-form in all the above-mentioned Decapoda, its existence in Peneus during the whole of that period of life which is richest in progress and in which the wide gap between the Nauplius and the Decapod is filled up, its recurrence even in the development of the Stomapoda, the occurrence of a larval form closely approaching the youngest Zoea of Peneus in the Schizopod genus Euphausia, and the reminiscence of the structure of Zoea, which even the adult Tanais has preserved in its mode of respiration, -- all indicate Zoea as one of those steps in development which persisted as a permanent form throughout a long period of repose, perhaps through a whole series of geological formations, and thus has also made a deeper impression upon the development of its descendants, and formed a firmer nucleus in the midst of other and more readily effaced young states.